Variable resistors



Nov.A 11, 1969 w.- D. KI'RKENDALL VARIABLE RES I STORS 2 Sheets-Sheet 1 Filed Dec. 1, 1966 INVENTOR 'ORNEYS WILL/AM D. K/R/fE/VDALL N0V- 11, 1969 w. D. KIRKENDALL 3,478,294

VARIABLE RES I STORS Filed Deo. l, 1966l 2 Sheets-Sheet 2 *if INVENTOR.

W/Lmm K/,e/ENDALL A TURN/Ys United States Patent O VARIABLE RESISTORS William D. Kirkendall, Dalton, Pa., assignor to Weston Instruments, Inc., Newark, NJ., a corporation of Delaware Filed Dec. 1, 1966, Ser. No. 598,416

Int. Cl. Hille 5/02 U.S. Cl. 338-174 13 Claims ABSTRACT OF THE DISCLOSURE This invention relates to variable resistors'and is particularly applicable to miniature trimmerpotentiometers of the type having'an arcuate resistance element and a'rotary contact assocated therewith.

Although variable resistors and miniature potentiometers 1of this general type have long been known and are now widely used in various forms, problemsare still encountered in attempting to provide such devices which are truly satisfactory. Ordinarily, the resistor must include, in addition to the resistance element, a rotary drive member, a rotary contactmember to be driven by the drive member so as to traverse the resistance element, and some sort of clutch or slip device which will allow the drive member to continue to rotate after the contact member, having reached an end of the resistance element, is held stationary. It is accordingly Iusually necessary to employ a contact member which is an element separate fromthe drive member, and a spring-like'member to maintain driving relation between the contact member and the drive member. One particular problem has been that of maintaining the Adrive member concentric with the contact member'and the spring member, particularly `Ain those potentiometers wherein the contact memberis carried by, as well as driven by, the drive member. Additionally,

contact members have taken on relatively complexconiiof the type described, in which a ydrive member and a n rotary contact member are held in properi engagement by spring forces developed in the' contact member byreason of its engagement between the drive member and a stationary bearing surface presented by the conductive return means for the rotary contact member.

Another object is to provide such a-potentiometer in which a drive member and a contact member engage each other in such fashion as tov provide a slip-clutch action when rotation ofthe drive member is continued after the contact member has reached one limit of its travel, the spring forces necessary to attaindriving engagement and slip-clutch action being developed wholly within' the contact member as a result of the manner in which that bearing surface for the contact member.

ice

Another object is to provide, in a miniature potentiometer of the type described, improved slip-clutch means of the recess-and-protuberance type.

Another object is to devise a miniature potentiometer of the worm wheel driven rotary contact type having improved means for maintaining proper coaxial alignment between the worm wheel, the rotary contact member, and a bearing surface with which the contact member is engaged.

Another object is to provide a miniature potentiomete of the type described, which employs a spring washer for the purpose of reducing to a practical minimum thespn'ng forces in the contact member.

Broadly stated, potentiometers according vto the invention comprise a housing defining an internal cavity; a worm wheel or equivalent drive member mounted on the housing for rotation about a xed axis and having at least one side exposed within the cavity of the housing; a resistance element within the housing andextending arcuately concentric with the axis of rotation of the drive member; a rotary contact member having a body formed of thin spring sheet metal and disposed in the housing adjacent the inwardly exposed side of the drive member; and an electrically conductive return means for the rotary contact member. The return means comprises a lead element which has an end portion presenting a bearing surface which is centered on the axis of rotation of the drive member and disposed on the side of the body of the contact member which is opposite the drive member. An outer peripheral portion of the body of the contact member engages the drive member and the return means engages the body of the contact member in an area which is spaced concentrically inwardly of the outer peripheral portion. The body of the contact member is resiliently deformed, by reason of such engagement between the drive member and the return means, with this resilient deformation establishing a spring force effective to maintain proper driving engagement between the drive member and the rotary contact member.

In one embodiment of the invention, the body of the contact member is in direct slidable engagement with the bearing surface presented by the lead element. In another embodiment, a resilient member is interposed between the body of the contact member and the bearing ysurface in such fashion as to reduce to a minimum the spring forces in the body of the contact member.

In order that the manner in which the foregoing and other objects which are achieved in accordance with the invention, can be understood in detail, particularly advantageous embodiments thereof will be described with reference to the accompanying drawings, which form a part ofthe original Idisclosure of this application, and wherein:

FIG. 1 is a perspective view of a completelyassembled miniature potentiometer in accordance with one embodiment of the invention;

FIG. 2 is a plan view of the potentiometer of FIG. l, with a portion of the housing ibroken away for clarity of illustration;

FIGS. 3 and 4 are transverse sectional views taken respectively on lines 3-3 and 4 4, FIG, 2;

FIG. 5 -is a sectional view taken on 1ine\5-S, FIG. 3;

FIG. 6 is an elevational' view of a worm wheel employed in the potentiometer, taken from the side ofthe wheel exposed toward the interior of the housing;

FIG. 7 is a sectional view taken on line 7-7, FIG. 6;

FIGS. 8 and 9 are plane and'edge elevational views, respectively, of the rotary contact member `of the" potentiometer;

FIG. 10 is a side elevational view of the worm or lead screw employed in the potentiometer; A

\ FIGS. 11-13 are perspective views of lead elements employed-in the potentiometer;

FIG. 14 is a perspective view of a modified form of lead element which can be employed in the potentiometer; FIG. l5, similar to FIG. 3, is a partial sectional view of-the interior. parts -of another embodiment of the potentiometerutilizing the lead element of FIG. 14 and a spring-like member; and FIG. -16 is a perspective view of the spring-like member of FIG. 15.

Referring to the drawings, the embodiment of the invention villustrated in FIGS. 1-13 comprises a housing1-FIGS.-15, of square plan configuration and rectangular transverse cross-section. The housing is made up of a-base portion 2 and a top or cover portion 3, both molded as integral units from a suitable rigid synthetic resinous ,material of good electrical insulating properties, such as.=glassilled diallyl phthalate. For convenience of reference, base portion 2 will be considered as having a flat bottom wall 4, flat side walls 5, 6 land 7, and a shorter-side wall 8, the base portion being notched at each end of wall 8 as seen in FIG. 5. The inner side surface 9, FIG.5, of the base portion extends cylindrically and .at right angles to the fiat inner surface 10 of bottom wall 4, surfaces 9 and 10 delining a cup-shaped recess which opens toward top portion 3 in the assembled housing. The diameter of surface 9 is only slightly smaller than the space between the outer faces of side walls and 7, and the inner surface and the outer faces of the side walls accordingly -dene corner portions 11-14, FIG. 5, which are generally triangular in plan.

The side wall portion 15, FIG. 5, between shorter side Wall 8 and wall 7, the side wall 7, and that portion of side wall 6 extending from wall 7 to a point near wall 5, are all of a height only slightly less than the overall height of the housing. The remaining portion of side wall 6, all of side walls 5 and 8, and the side wall portion 16, FIG. 5, between walls 8 and 5, are all of a height significantly shorter than the other side portions of the base. Shoulders at 17 and 18, FIG. 5, join the portions of `different height.

Base portion 2 also includes a center post projecting from inner wall toward top portion 3, in the assembled housing, the center post being coaxial with cylindrical wall 9 and including a base portion 19, FIGS. 3-5, of larger diameter and a tip portion 20 of s maller diameter, the two portions being joined by a flat transverse annular shoulder 21.

The upper edge of side Wall 8 is provided with a notch 22 disposed radially with respect to cylindrical wall 9 10, and a portion 27 joined only to surface 10, as will `be clearfroma comparison of FIGS, 3 and 5. Flange portions 27 are provided to assure that there will be no bridging electrical contact, as by solder, between the two endsof the resistance element later described. Flange portions .261serve as stop members, as hereinafter explained. The upper edge of side wall 8 is also provided with notches 28 and 29, FIG. 5,.located respectively adjacent the ends of Wall 8. Notch 28 communicates with an enlarged groove 30 in surface 9 and a groove 31 in surface 10: Notch 29 similarly communicates with an enlarged groove 32 in'surface 9 and a groove 33 in surface 10. The combination of notch 28 and grooves 30 and 31 lies in a.- common radial plane which includes the longitudinal axis of the' center post, and the same holds true for the combination of notch 29 and grooves 32 and 33.

At a point near the junction of side walls 5 and 6,

corner portion 12 is provided with a straight ridge 34, FIG. 5, which extends at right angles to side wall 5 and is spaced from side wall 6. Ridge 34 is of significant height, projecting toward top portion 3 in the assembled housing, and presents a transversely rounded upper edge. That part of corner portion 12 between shoulder 18 and ridge 34 is shorter than the portion of side wall 5 extending from ridgel 34 toward wall portion 16, and presents a liat upper' surface 35 which intersects wall 9, so that ridge 34 and' shoulder 18 are spaced across a notch in wall 9.

Top portion 3 (FIG. 2) comprises a flat top wall 36 and fiat side walls 37-40. Side wall 40 is provided with a rectangular opening 41, FIG. 1, of such size and configuration as to snugly accommodate Wall 8 of base portion 2. In the assembled housing, top portion 3 is telescopically engaged over base portion 2, with side Walls 37-39 of the top portion lying in face-to-face engagement with side walls 5-7, respectively, of the base portion, and with side wall 40 lying in face-to-face engagement with wall portions 15 and 16 and snugly embracing'that portion of the base portion which defines wall 8, as will be clear from FIGS, 1 and 5.

A cylindrical center post 42 (FIGS. 3 and 4) projects from the top wall 36 coaxially toward tip portion 20 of the base portion `when the housing is assembled, the lengths of the two center posts being such that, in the assembled housing, the tips of the two vcenter posts are spaced slightly apart. At the intersection between side walls 37 and 41 and top wall 36, top portion 3 includes a Iboss 43, FIG. 2, having an elongated recess 44 opening axially toward side wall 38. At the junction between side walls 37 and 38 and top wall 36, portion 3 includes a boss 45 having a cylindrical bore 46, FIG. 2, opening both toward boss 43 and through side wall 38, bore 46 being coaxial with recess 44. When portions 2 and 3 are properly assembled, with the edges of Walls 37-40` lying in the plane of the outer surface of wall 4, there is a substantial space between wall 36 and the top of wall l5 throughout the length of wall 5, and this space is of increased depth in the area of corner portion 12 between ridge 34 and wall 38.

Adjacent bottom wall 4 the side wall of base portion 2 of the housing is of increased thickness, and a continuous fillet 9a, FIGS. 3 and 4, is provided. An arcuately extending resistance element 47 is secured to llet 9a and inner surface 10 of wall 4, as by epoxy cement. Resistance element 47 extends for almost a complete circle, its ends being disposed respectively adjacent flange portions 26, as will Ibe clear from FIGS. 3 and 5. Flange portions 26 project inwardly from surface 9 an amount at least 4equal to the cross-sectional width of the resistance element. Resistance element 47 can be of any suitable type, a conventional wire wound element being employed in this embodiment. n

'The combination of` notch 28 and grooves 30 and 31 accommodates the appropriate portions of a terminal lead 48, shown in detail in FIG. l2. Lead 48 includes a continuous length of round conductive wire comprising a straight exterior portion 49, a -straight portion 5.0 extending through notch 28, a straight portion 5 1 at right angles to portion 50 and extending through groove 30, and an end portion 52 disposed in groove 31. End portion 52 is flattened and so disposed that its llarger transverse dimension extends parallel to wall 10. The relative dimensions of end portion 52 are such that the same engagesl the ad jacent end portion of resistance element 47 and projects inwardly therebeyond. End portion 52 isl connected mechanically and electrically to the resistance element by a solder joint 53, FIG. 5. A second terminal lead 54, FIG. 13, similarly includes a straight exterior portion 55, a straight portion 56 extending through'notch 29, a` portion 57 at right angles to portion 56 and extending through groove 32, and a liattened end portion 58 disposed in groove 33 and connected to the corresponding end porti'on of resistance element 47 by a solder joint 59. Exterior portions 49 and 55 extend parallel'to each other, as seen in FIGS. 1 and 5. n

The potentiometer comprises a third lead 60,*FIG. 1l, including a straight exterior portion 61 which extends inwardly through notch 22, a straight'portion 62 at right angles to portion 61 and accommodated in groove 24, a straight portion 63 extending through groove 25, a straight portion 64 extending upwardly through groove 23 inthe base portion 19 of the center post of base 2, and an end loop 65 lying in a plane at right angles to portion 64 and encircling tip 20 of the center post so as to lie against shoulder 21. Lead element 60 isof circular'transverse cross-section.

' The' moving system of thepotentiometer comprises a worm wheel 66, FIGS."2-4, a rotary contact member 67, and a lead screw or worm 68. Wheel 66'is formed as an integral unit of diallyl "phthalate, or otherrrigid material of good electrical insulating properties, and comprises a circular body having a cylindrical central opening 69, FIG. 7, and a toothed periphery 70. A shallow circular recess 71, concentric with opening 69, is provided in one of the flat surfaces of the wheel, so that aysmooth flat annular surface 72 is presentedfor engagement with top wall 36 when they wheel vis properly disposed withthe cylindricaly -wall of opening 69 slidably embracing center post 42. Theopposite face ofv -wheel'66 is formedfwith a`shallow circular recess 73, concentric with opening 69, and a circularly spaced series of individual recesses 74, best seen in FIG. `6, which extend radially of `the wheel, open inwardly through the periphery of recess 73, and extend outwardly nearly to they location of the peripheral teeth of the wheel. The face of the wheel comprising recesses 74 is completed 'by an annular ilange 75 which extends outwardly beyond the teeth of the wheel.

As seen from FIGS. 8`and,9, rotary contact member 67 is formed as an integral sheetfmetal unit, advantageously beryllium-copper spring stock. In its relaxed or undistorted condition, illustrated in FIG. 9, member 67 comprises a flat circularqbody portion 76 havinga circular central aperture 77 of a diameter slightly largeithau that of center post tip portion 20. The diameter of body por; tion 76 is" slightly greater than jthediameter of recess 73. At two points ydiametrically opposed across opening 77, the peripheraledge of body 76 is deformedyto provide identical protuberances 78 which are of semi-circular transverse cross-section and of a lengthpradially of body 76, slightly less than that 'of recesses 74. While the outer ends of protuberances 78 open through the periphery of body 76, theinner ends thereof curve smoothly into the plane of the body 76`so as kto present rounded end surfaces 79 of generally spherical' nature'. Both protuberances 78 project from thefsauie side of body portion 76. Member67 is completed by a radiallyextending contact arm 80, the'root portion ofthe arm being eut from bodyr portion 76 by slits 80a, and the tip'p'o'rtion' projecting beyond thecircularxedge of the body portion and lterminating in a contact tip 81 of curved transverse cross-section. Arm 80 is bent from body portion 'V76 'so as to slant away from the side thereof opposite lprotuberances 78, and ltip 81 is'concave'relative to thebody portion 76. n

4 In the assembled potentiometer, as seen in FIGS. 3 and 4, rotary contact member 67 is'disposed between wheel 66 and the end loop 65 of lead 60, the tip portion 20 of the center post of base portion 2 extending throughcentral aperture,77 of the contact member. Since ltipportion and center post 42 are coaxially aligned, and since the cylindrical wall of the central opening 69 of wheel 66 slidablyiembra'ces center post 42, .the wheel and the rotary contact member are held in coaxial alignment, with the circular body portion 76 of the contact member centered with respect to recess 73 and the circular series of recesses 74. With: top portion 3 rfully engaged over base portion 2, so that side walls 6 and 7 engage wall 36, the space between end loop 65 of lead 60 and the plane defined by the bottom walls of recesses 74 is inadequate to accommodate the effective thickness of contact body portion 76 (including protuberances 78) in its normal llat undistorted condition. Since surfaces 79 of protuberances 78, adjacent the edge of body portion 76, engage the bottoms of two of the recesses '764, and since end loop 65 of lead 60 slidably engages' the other side of the contact body portion near the center thereof, body portion 26 is resilieutly distorted into a concavo-convex configuration, concave with respect to base portion 2, and with the central portion of the contact body curving into recess 73 and contact arm 80 slanting away from wheel 76 at such an angle that the rounded surface of contact tip 81 is resiliently held in sliding engagement with resistance element'47.

Lead screw 68, FIG. l0, includes a plain cylindrical tip 82, a threaded body portion 83, an enlarged cylindrical portion 84 having a transverse annular groove 85 of semi-circular transverse cross-section, a cylindrical portion 86 of smaller diameter, and a head 87. An O-ring 88 surrounds portion 86, being retainedpbetween portion 85 and head 87. In the assembled potentiometer, tip 82 of the lead screw is rotatably engaged in recess'44, and the combination of portion 86 and the adjacent parts of portion 84 and head 87 are journaled in bore 46 with O-ring 88 providing a seal between the lead screw and the housing and with head 87 exposed for manual manipulation. Ridge 34 is engaged in groove 85, once housing portions 2 and 3 are fully engaged, so that significant axial movement of the lead screw relative to the housing is prevented. The threads of body portion 83 mesh with the peripheral teeth of wheel 66, so that the wheel can be driven in either direction by turning the lead'screw in the appropriate direction.

Engagement of protuberances 78 in any diametrically aligned pair of the recesses 74 is resiliently maintained by the concavo-convex resilient deformation of contact body portion 76 and serves to provide a positive mechanical connection between wheel 66 and rotary contact member 67. Hence, so long as contact arm 80 is free to move along resistance element 47, rotation of wheel 66 is imparted directly to the rotary contact member.

Contact arm 80 is of such length that continued rotation of wheel 66 and member 67 causes contact tip 81 to come into lateral engagement with one of the flange portions 26. When such engagement occurs, stopping the rotary contact member, continued rotation of wheel 66 is allowed -because protuberances 78 are cammed out of the two recesses 74 in which they are engaged, such action resulting because of the transversely rounded configuration of the protuberances and the resilient nature of the rotary contact member. As rotation of wheel 66 continues, the protuberances engage in the next successive pair of recesses 74, are then cammed out of those recesses, and so on progressivelyl as the recesses are presented. However, when the direction of rotation of wheel 66 is reversed, contact arm 80 is again free to move, and engagement of protuberances 78 in recesses 74 is again eiective to maintain the desired positive drivf ing engagement between the wheel and the contact arm.

The embodiment of the invention thus far described has the advantage that the axially directed spring'forces which act to maintain the rotary kcontact member'properly engaged with the drive wheel, to allow a clutch action to occur when the contact arm is at the limit of its travel and rotation of the driving gear still continues,

in addition to the wheel, contact member, and lead,l and without the necessity foremploying a rotary contactmember hayin-g a special portion provided solely tol act as a spring. Further, it will be noted that lthe invention does not require extensive changes in the size or shape of the drive wheel and the rotarykcontrol member.

FIG. 14 illustrates a modified form of conductive lead whichy can be employed in the potentiometer of FIGS. 1-10. Here, the lead 160 is identical tolead 60, FIG. 11, save Athat the looped end 165 is provided by first flattening the end portion of the wire `to a thickness on the order, for example, of one third the diameter of the wire, so that the flattened end portion is of substantial width, and then piercing the flattened end portioncentrally to provide a circular opening 165a of such size as to snugly embrace the center post tip portion 20, FIGS. 3-5. Since the thickness of the attenedfend portion is substantially less than the diameter of the wire, shoulder 21, FIG. 4, must be moved a corresponding distance toward the tip 20 of the centenpost in order to assure an effective amount of deformation of the body portion of the rotary contact member in the assembled resistor.

FIG. 15 shows another embodiment of the invention, which is substantially identical in construction to the potentiometer of FIGS. 1410, but which employs the conductive lead 160 (FIG. 14) and a spring member 101. Spring member 101 is formed from a thin, circular disc of electrically conductive, resilient metal, and has a relaxed configuration (prior to assembly in the potentiometer) as shown in FIG. 16. Spring member 101 has a curved surface 102 and opposed peripheral surfaces 104. A circular opening 103 is formed centrally of spring member 101 and dimensioned so that the spring member is rotatable about tip portion of the center post.

Spring member 101 is disposed within the potentiometer housing so that the portion of its arcuate surface 102 around opening 103 slideably engages flattened end 165 of lead 160, and its peripheral surfaces 104 frictionally engage the concave surface of the resiliently distorted contact body portion 76 to be rotated therewith. Spring member 101 provides axially directed spring forces which reduce to a minimum the forces acting to distort the contact body portion 76. Since there is a reduction in the net axial forces acting on contact body portion 76, less force is required to rotate lead screw 68, resulting in increased life of worm wheel 66 and other parts of the potentiometers moving system.

As seen in FIG. 15,- the concentricity of worm wheel 66 with rotary contact member 67 and flattened end 165 of lead 160, is maintained with the use of spring member 101. Spring member 101 does not serve the usual function that springs of prior potentiometers serve, the function of prior art springs being to maintain driving engagement between a drive member and a contact member. Rather, spring member 101 reduces to a minimum the axial forces acting on contact body portion 76, so that less forces is required to operate lead screw 68, and is not needed to maintain driving engagement between drive wheel 66 and contact member 67.

While particularly advantageous embodiments of the invention have been disclosed for illustrative purposes, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. In a miniature potentiometer, the combination of housing means defining an internal cavity having two spaced parallel surfaces; a drive member mounted in said housing for rotation about an axis at right angles to said surfaces, one side of said drive member slidably engaging one of said surfaces, the other side of said drive member facing the other of said surfaces, said other side of said drive member having an annular series of spaced recesses centered on said axis, the recesses of said series being spaced apart and elongated radially relative to said axis; a conductive bearing element supported on said other surface and presenting a bearing surface exposed toward said drive member, the extent of said bearing` surface transverse to saidpaxis being `small as compared to the diameter ofsaid series of recesses; an integral rotary contact member of spring sheet metal comprising` a circular body portionl and a contact arrnl projecting generally radially from vsaid body portion, said body portion having a radially elongated protuberance'locatedin the peripheral edge semicir'cular transverse cross section andv having an inner end surface which is of generallyspherical configuration, said contact member being disposed'betweenlsaid drive member and .said bearing surface with saideprotuberance protruding from the side thereof adjacent said drive merriberand with said circular' body portion centered o n` said axis, the radial space vbetween said protuberance and said axis being such thatv said protuberance can engage in any one ofy said recesses depending upon the relative rotational positions ofsaid drive member and said contact member, said bod-y portion of said contactmember being at, save for said protuberance, whenin relaxed undistorted condition,nthe effective axial space between said vdrive member and saidbearing surface being insufficient to accommodate saidbody portion when the same is in said relaxed condition, said bearing surface engagingthe `centralportion of said body portion on the side thereof opposite'said drive member, and said body portion therefore being resiliently distorted into concave-convex configuration, convex relative tosaid drive member, such that the spring force resulting from such'distortion maintains said generally spherical'inner end surface of said protuberance in engagement with the wall of one of said recesses; and an annularly extending resistance element supported in said cavity concentric with said axis and in a vposition spaced from said other side of said drive member, said contact arm extending into sliding engagement with said resi's tance element.

2. IIn ak miniature potentiometer, the combination of housing means defining an internal cavity having a relative top surface spaced parallel from a relative'bottom surface; a drive member mounted in said housing for rotation about an axis 'at right'angles to said parallel surfaces, one side of'said drive member slideablyengaging said top member surface, the other side of said drive member facing said bottom surface, said other side of said drive member having an annular seriesiof spaced 'recesses' centered on said axis, the recesses of said series being spaced: apart and elongated radially relative'to-said axis; a conductive bearingelement supported on said bottom surface and presenting a bearing surface exposed toward said drive member, the extent of said bearing surface transverse vto said'axis being small as, compared to the diameter of said series ofrrecesses; an integralrotary contact member yof resilient material including a circular body Yportion and a contactarm projecting generally radially from s aid body portion, said body portion having at least one. radially elongated protuberance located -in the peripheral edge portion thereof, said protuberance being of generally semi-r circular` transverse crosssection and having an inner end surface which is of generally spherical configuration, said contact member being disposed in said housing means so that said protuberance protrudes `from the side thereof adjacent said drive'member and -with saidv circular body portion centered on said axis, the Vradial space between said protuberance and said axis being such' thatsuch protuberance can engage in any Vv'of said recesses-depending upon the relative rotational positions of `said drive member and said contactmember, said bodyv portion of said contact member being fiat, save for said protuberance, when in a -relatively undistorted condition; a resilient membercentrally-disposed about said-axis, having a surface'which slideably engages said bearing surface, and peripheral surfaces which frictionally engage the central portion of said body portionon the side thereof opposite said drive member, said body portion being resiliently distorted into concavo-convex configuration, convex relative to said drive member, such that tlie spring force resulting from such distortion maintains said generally spherical inner end surface of said protuberance in engagement with the wall of one ofthe recesses; and an annularly extending resistance element supported in said cavity concentric withl said axis and in a position spaced from said other side of said drive member, said contact arm extending intol sliding engagement with' said resistance element.

3. The combination defined in claim Z, lwherein a first supporting post extends into said cavity from said bottom surface and has Va tip portion projecting in alignment with said axis; said bearing surface defines an opening through which said tip portion extends; said body portion of said contact member has a central opening through which said tip portion extends; said resilient member has a central opening through the surface which slideably engages said bearing surface, said tip portion extending through said central opening; a second supporting post extends from said other of said parallel surfaces and projects toward said tip portion in axial alignment with said axis; and said drive member has a central opening through which said second post extends.

4. The combination defined in claim 3, wherein said lead element is a wire and said bearing surface is presented by a flattened portion of the wire.

5. The combination defined in claim 4, wherein said resilient member has a curved surface, said resilient member also presenting peripheral surfaces which frictionally engage said body portion of said contact member.

6. The combination defined in claim 5, `wherein said resilient member, if stressed to a flat condition, would have a substantially circular configuration, so that when said resilient member is disposed on said tip portion at least two opposed peripheral surfaces of said resilient member will frictionally engage said body portion of said contact member, and the central portion of said curved surface about said central opening therein will slideably engage said bearing surface.

7. In a miniature potentiometer, the combination of housing means defining an internal cavity having two spaced parallel walls; a drive member Imounted in said cavity for rotation about an axis at right angles to said walls, one side of said drive member facing one of said walls and said one wall being operative to limit movement of said drive member toward said one wall in the direction of said axis, the other side Iof said drive member facing the other of said walls and having an annular series of spaced recesses centered on said axis; electrically conductive return means supported on said other wall and comprising a lead element which extends outwardly from said cavity and a bearing surface which is exposed toward said drive member; an integral rotary contact member of spring sheet metal comprising a body portion, which is generally centered on and extends generally transversely of said axis, and a contact arm projecting generally radially from said body portion, said body portion having a protuberance located in the outer edge portion thereof, said protuberance projecting from one major face of said body portion and being spaced radially from said axis by a distance such that said protuberance can be engaged in any of the recesses of said annular series of recesses, said protuberance having a generally semicircular cross-section in a direction transverse to a line extending radially from said axis and through the center of said protuberance, the portion of said protuberance directed toward said axis being of generally spherical configuration, said contact member being disposed between said drive member and said return means with said protuberance facing toward said drive member, said drive member having an annular outer portion which includes said recesses and is engaged by said outer edge portion of said body portion of said contact member, said return means engaging the central portion of said body portion of said contacty member; said body portion of said contact member having a relaxed condition and the effective axial space between said annular outer portion of said drive member and said return means being insufficient to accommodate said body portion of said contact member when said body portion is in said relaxed condition, said body portion of said contact member therefore being resiliently distorted into concavoconvex configuration, convex to said drive member, in such fashion that the spring force resulting from such distortion maintains said generally spherical portion of said protuberance engaged in one of said recesses when .the relative rotational positions of said drive member and said contact member are such that said protuberance registers with such recess; and an annularly extending resistance element supported in said cavity concentric with said axis in a position spaced axially from said other side of said drive member, said contact arm extending into sliding engagement with said resistance element, said bearing sur'- face of said return means allowing said contact member to turn with said drive member when the latter is rotated and said protuberance is engaged in one of said recesses.

8. The combination defined in claim 7, wherein said lead element of said return means has an inner end por'- tion which is fiat, transverse to said axis, and presents said bearing surface; and said return means comprises a curved resilient member having an arcuate surface slidably engaging said bearing surface and peripheral surfaces frictionally engaging said body portion, said curved resilient member being axially resiliently distorted between said contact member and said bearing surface and rotating with said contact member when said contact member is rotated by said driving member.

9. The combination defined in claim 8, wherein said inner end portion of said lead element, said curved resil ient member, and said body portion of said contact member are each provided with a post projecting toward said one wall in alignment with said axis, and said post extends through said apertures.

10. The combination defined in claim 9, wherein said post includes a transverse shoulder and at inner end portion of said lead element is seated on said shoulder.

11. The combination defined in claim 9, wherein said lead element is a wire and said inner end portion is a attened portion of said wire.

12. The combination defined in claim 7, wherein said lead element is a wire of circular transverse cross-section and said inner end portion is a circularly extendingv loop which is concentric with said axis and lies in a plane transverse thereto, said circularly extending loop presenting said bearing surface and being slidably engaged directly by said body portion of said contact member.

13. In a miniature potentiometer, the combination of housing means defining an internal cavity; a drive wheel carried by said housing means for rotation about a fixed axis, said drive wheel having one side which faces the interior of said cavity and extends transversely of said axis, said one side of said drive wheel having a central recess and an annular series of spaced smaller recesses disposed outwardly of said central recess; electrically conductive return means including a portion mounted on said housing means within said cavity, said portion being 1ocated at said axis and facing toward said one side of said drive wheel; an annularly extending resistance element mounted within said cavity concentric with said axis in a position spaced from said drive wheel in the direction in which said one side faces; and an integral rotary contact member of spring sheet metal comprising a body portion and a contact arm, said body portion vbeing of larger plan dimension than is said recess, said body portion being centered on said axis and disposed between said portion of said return means and said drive wheel, and said contact arm projecting from said body portion generally radially with respect to said axis, said body portion having a protuberance spaced outwardly from said axis by a distance such that said protuberance can register with and engage in one of the recesses of said annular series, said protuberance projecting from the plane of said body portion toward said drive wheel; the eective space between said one side of said drive wheel vand said portion of said return means being inadequate to accommodate said body portion of said contact member, when said body portion is in relaxed condition, said body portion of said contact member therefore being resiliently distorted into concavoconvex configuration, convex relative to said drive wheel, with said body portion curving into said central recess, the spring force resulting from such distortion maintaining said protuberance operatively engaged in one of said recesses 0f said annular series when the relative rotational positions of said drive wheel and said contact member are such that said protuberance registers with such recess, said contact arm extending into sliding engagement with References Cited UNITED STATES PATENTS 3,105,217 9/ 1963 Ferrell et al. 338--174 3,124,778- 3/ 1964 Youngbeck 338--174 3,201,737 8/ 1965 Mathison 338-174 3,369,208 2/ 1968 Kirkendall 338-174 LEWIS H. MYERS, Primary Examiner A. T. GRIMLEY, Assistant Examiner 

